(1) Field of the Invention
The present invention relates to a compressed air manufacturing facility provided with a compressor driven by an electric motor in which a rotating speed is variably controlled by an inverter.
(2) Description of Related Art
The compressed air manufacturing facility is provided with a compressor compressing an air, for example, serving as a variable speed compressor unit executing a capacity control, an electric motor driving the compressor, an inverter variably controlling a rotating speed of the electric motor, a pressure sensor detecting a discharge pressure of the compressor, and a control apparatus variably controlling the rotating speed of the electric motor via the inverter on the basis of a deviation between the discharge pressure detected by the pressure sensor and a control pressure. Further, as a structure provided with a plurality of variable speed compressor units, there have been know a structure in which the units are operated in parallel, and a structure in which the units are operated alternately and in a following manner. Further, for example, in a structure provided with a plurality of compressor units including at least one variable speed compressor unit, there has been known a structure in which one variable speed compressor unit is operated by variably controlling a rotating speed of a corresponding electric motor via an inverter, and the other compressor units are switched to a full-load operation state at a rotating speed which has an upper limit of the rotating speed of the corresponding electric motor or a stop state, thereby controlling a number of the units.
In this case, a pressure loss of a discharge air system supplying the compressed air discharged from the compressor to a supply end is changed in correspondence to a change of an amount of a discharge air of the compressor and an amount of a used air of the supply end. Accordingly, in general, a control range of the discharge pressure of the compressor at an upstream side position of the discharge air system is set by anticipating a maximum pressure loss of the discharge air system in such a manner that a terminal pressure (a supply pressure) at a downstream side position of the discharge air system comes to a desired pressure value or more. In the compressed air manufacturing facility mentioned above, it is possible to obtain a desired compressed air, however, for example, in the case that the amount of the used air is small (that is, the amount of the discharge air of the compressor becomes smaller), the control range of the discharge pressure of the compressor is kept high in spite that the pressure loss of the discharge air system becomes smaller. Accordingly, the compressor is driven more than necessary, and an extra power is consumed.
Accordingly, in order to correspond to this problem, for example, there has been proposed a control apparatus variably controlling a rotating speed of the electric motor in such a manner that the terminal pressure at the downstream side position of the discharge air system comes to a predetermined range in correspondence to the discharge pressure of the compressor at the upstream side position of the discharge air system detected by the pressure sensor (for example, refer to JP-A-2004-190583). Describing in detail, the control apparatus previously stores a pressure loss (=discharge pressure of the compressor at the upstream side position−terminal pressure at the downstream side position) of the discharge air system at a time of a specification pressure, and is structured such as to compute a pressure loss of the discharge air system on the basis of a ratio between the discharge pressure of the compressor detected by the pressure sensor and the specification pressure. Further, the structure is made such as to compute the control range of the discharge pressure of the compressor obtained by adding a computed value of the pressure loss of the discharge air system to a predetermined range of the terminal pressure at the downstream side position of the discharge air system, and variably control the rotating speed of the electric motor on the basis of the computation.